A 1.3-GHz IF digitizer using a 4/sup th/-order continuous-time bandpass /spl Delta//spl Sigma/ modulator

We present a 4/sup th/-order, 3-bit, 4.3 GHz continuous-time bandpass /spl Delta//spl Sigma/ modulator (CT-DSM) that can directly digitize a 1.3-GHz IF signal. We used the impulse-invariant transform to design the CT-DSM, which has a similar NTF (noise transfer function) as an idealized discrete-time modulator despite up to 1.6 clock delays in its feedback loop paths. The part was fabricated using InP HBT technology, and has a measured SNDR of 39 dB in a 200 MHz bandwidth.